1. Field of the Invention
The present invention belongs to the technological field relating to a gas jet cooling device, especially to a gas jet cooling device for a steel strip in a continuous annealing furnace.
2. Description of the Related Art
JP-A No. 116724/1987 describes a gas jet cooling device for a steel strip in a continuous annealing furnace. The gas jet cooling device for a steel strip in a continuous annealing furnace described in the document is, with the aim of preventing the flow rate of a gas blown onto a steel strip from attenuating, configured so that: the distance a between the steel strip and the tips of nozzles may not be more than 70 mm and the length b of the nozzles protruding from the front face of a windbox may not be less than (100−a) mm; thereby the gas after blown onto the steel strip may be discharged into the free space in the furnace (the space excluding the space between the steel strip and the tip faces of the nozzles in the furnace); and resultantly the gas after blown onto the steel strip may less disturb the flow of the gas blown through other nozzles. Note that, the windbox is described under the term “cooling gas chamber” in the document.
Since the gas jet cooling device for a steel strip in a continuous annealing furnace described in JP-A No. 116724/1987 is configured so that the distance a between the steel strip and the tips of nozzles may not be more than 70 mm and the length b of the nozzles protruding from the front face of a windbox may not be less than (100−a) mm as stated above, the distance between the steel strip and the front face of a windbox is not less than 100 mm, thus the distance between opposing windboxes interposing the steel strip in between is not less than 200 mm, and the cooling chamber must be large accordingly. Note that, the cooling chamber is described under the term “furnace chamber” in the document.
When the size of a cooling chamber increases, the mass of an insulator per unit cooling length of the cooling chamber also increases, thus the thermal capacity thereof increases, and thereby the responsiveness (the thermal inertia) of the temperature in the cooling chamber lowers. As a result, when the steel strips the intended mechanical properties of which are different from each other are continuously processed and thus the cooling conditions are different between the preceding steel strip and the succeeding steel strip, the controllability of the intended cooling end temperature of each steel strip lowers and moreover the mechanical properties of each product can hardly be secured. Further, another arising problem is that it causes the construction cost of a cooling chamber to increase.